HELP! Noise + noise = :-(

[stand]

Hi!

Last night I finally finished my first project – Metal Simplex pedal. After solving some problem with cold joint/bad soldering I've got the sound that I needed – powerful, long sustained, nice... I tried to include BC550C instead of original 2N3904 transistors, and finally found most pleasant combination (Q1= BC550C, Q2=2N3904) and green instead of red LED. But... (there is always some "but" that drives us crazy...).

So, there is something I had to ask all of you who know about pedals so much. Here are my problems:

1)   I've got lots of noise but most of it lasts as long as I keep my hands off guitar or any metal on guitar (strings, tuners, jack...).As soon as I touch strings – this noise stops. I don't know what's hum but I'd describe this noise as similar to noise of hot oil in pan.
2)   There is also some radio noise (like somewhere between stations). It's very strange – when tone control of any of 2 pickups (I use single coils)  is on "zero" this noise disappears, but as soon I add a 10% of tone control on that "zeroed" pickup – noise immediately appears. It happens no matter which pickup you try. It's really mystery for me...
3)   Finally, this is something probably well known – when I decided to put it all in the plastic box/housing I was so disappointed – I've got much higher noise level, and I'll probably have to do something about wires – they're obviously too long and unshielded. But, it isn't all – when protoboard is out of the box and all parts are on the table sustain is very, very long and pleasant, distortion is stable and powerful. But, as soon as I put it all in the box (especially when I set up gain pot in its hole on front side) sustain is much shorter and it seems like signal is loosing its strength. Then distortion is somehow unstable, it looks like it is pulsing in unequal intervals. I am quite sure that contacts on protoboard are OK since it works well on the table and it is not squeezed in the box at all. I just have noticed that sound is better when I move gain pot away from other two pots (volume and tone).

What should I do to avoid these two different noises as much as possible? I don't expect to get noiseless distortion pedal but it seems really too noisy to me. Should I do experiments with only cable (without guitar) to see if then some noise will appear/disappear?

Finally, this could be important – no noises at all when I connect "bare" guitar into amplifier, no matter if I touch the strings or not. I get these noises only when I use Metal Simplex... 

Any ideas?

Dejan

[deadsnake]

When you place you hand on the strings you ground the circuit of the pickups and everything else. What you need to do is to ground everything that should be grounded. This is obvious but check this out:
this is shielding it prevents frequencies to scramble you circuit signals. can you see the aluminuim foil covering the inside.
http://diyguitarist.com/Images/WTS808-8.JPG

If you have a enclosure made of steel aluminium or anything else conductive you should connect the battery(or power supply) (-) pole to the enclosure and everything else that needs grounding should be grounded from the enclosure. Your circuit has to be grounded, so ground it to the enclosure instead of directly to your power supplier. This is the most effective way of reducing noise. Cosed circuits especially audio circuits are very sensible to touch and high frequencies. Shielding and proper grounding are the best ways to deal with them.

You said that you are using a single coil pickup. They are a bit noisy compared to humbuckers, that's why they are called hum-bucker. I don't know much about single coil guitars but I'm sure they make more noise than humbuckers.

[343 Salty Beans]

in a humbucker pickup, there are two coils which feed off of each other's frequencies. With a single coil pickup, it tends to grab onto something else's frequencies, especially fluorescent lights and other common electronics. I forget which frequencies it's feeding off of, but I think it's EM. Don't hold me to that though.

[stand]

To deadsnake:

Thanks for your advices; I'll see what I can do about it. I hope that you'll be so kind to give me few instructions about these noise-related problems. I hope that my questions (see below) are not very boring...

About "ground everything" – how should I do it? Metal Simplex is very simple circuit (http://www.diystompboxes.com/pedals/mtlsim.bmp) where just 2 transistors, one capacitor and volume pot are connected to the ground (grounded). I did it this way: Input and output negative poles are connected to the ground at the same single point with volume pot. Both transistor emitters and one cap are connected with this "ground point" by one wire from pin to pin. Should I connect these emitters and cap with this point with separated short wires to get star-like wiring and just one common point for whole ground in this circuit. How could I ground everything otherwise? Finally, could be this ground noise caused by amp. If it is, why there is no such noise when I don't use pedal?

About shielding – I use plastic box (lack of money at this moment, sorry...) so no metal enclosure here to shield circuit from unwanted frequencies. I'll try this trick you showed me on that picture – I'll stick Al - foil on all walls of this box, maybe it will do the job... Or maybe I just should find some can to do better shielding and to ground everything this way... Or maybe I am quite wrong about it?

I don't mind if my pickups are noisy – this is something I have to learn to live with, but this really doesn't sound like some quiet mmmmm or sssssss... It's loud and annoying. And I don't think this noise must be there. I'll start my fight against it and I hope that I can get some good results with help of DIY forum members. I don't have anyone else here who knows about these things (pedals) so you're my last hope...

To 343 Salty Beans:

I don't worry if it pick up some noise as long as it is bearable, but here I have two noises which are very loud and btw. these noises are not present without pedal...

[deadsnake]

It's almost 99% sure it's your pedal when you told me this doesn't happens when you plug your guitar straight to your amp. So do this look at the common ground point on your board, since you don't have a metal enclosure try linking your common ground point to a big metal piece of some kind for a while just for testing purposes. You don't have to desolder or solder anything to do this just use a wire of some sort and connect your common ground point to a big piece of metal and power in your metal simplex as usual. Test it see if you get the same thing. If you do then you might have to shield your plastic enclosure and then ground the aluminium fold as well foil as well. It doens't really matter the wiring in this case. The option you showed could be done too. But there is no need for it since you can simply use the wire I told you and hook it in a metal piece (it can't be that small). When you shield your enclosure find a metal piece of any kind that fits the bottom of your pedal. Take a look at this post, it's about a guy who didn't shield well his pedal. It's sure to help you.

[Transmogrifox]

All the symptoms you have described are very indicative of radio noise on the input.  Your guitar is acting as an antenna, and the Simplex (most distortion pedals in general) is a very good radio receiver, given that it has high gain, and distorts assymetrically.  The noise you hear is noise modulated onto RF carriers (similar to what you hear when you tune a radio to an unused station).  Your Metal Simplex doesn't care what it demodulates...it's probably demodulating any and all that your guitar picks up.  You may hear noise sometimes, other times radio, and other times hiss or squeals.

For the guitar, it's just the nature of the beast.  Grounding & shielding is better in some than others.

Where you can make the difference is on the input of the Metal Simplex:

1.  Plastic boxes are no good.  Use a metal box, or the aforementioned aluminum foil lining on the inside of your box (and connect the foil to ground somewhere).

2.  You can have a perfectly shielded box, and everything well grounded, but if there is RF on the signal conductor of your cable, it's already on the inside.  You then need to filter radio frequencies before they get demodulated by the pedal (demodulated=translated into audio frequencies).  There are a few things you can try.  I think the first thing that you should do is just connect a small valued capacitor (ceraminc) like 47 pF between the input of the circuit and ground.  For simplicity, you may simply solder it between the tip and ring connections on the input jack directly.

3. If that doesn't get rid of the noise, then add a ferrite bead on the signal input wire to the board, and also on your power supply (if you're using an external supply vs. battery).  These can be purchased from Digikey or Mouser, and they just snap around the wire so you don't even need to do any desoldering or cutting.

4. If all that fails, it may be entering through the power supply, and you need to filter the power in the same way--by adding capacitors from +9V to ground, and adding a ferrite bead on the "+9V" wire to the input of the board.

If all else fails, build an all-metal hut that is buried 30 FT. underground and move all your gear inside, shut the door, and use a UPS for power filtering.  Inside that shack, radio won't get to you.    (just kidding)

[stand]

Just short addition:

To test what causes hum petemoore's idea is:

"Get hum, unplug guitar.
Still hum, guitar is source.
Cable test, same way".

I must admit that I cannot understand it (though it's written in plain English...).
If I have hum with unplugged guitar then how guitar can be source of hum? And, about cable, should it be this way:

Get hum, unplug cable.
Still hum, cable is source.

I am probably stupid so I can't understand what Pete tried to say... Simple explanation for us dummies, anyone?

And, about strings shielding (as "cure" for noise that stops when we touch the strings or other metal parts) – noise stops when I touch ANY metal part including banana jack connector. I am sure that my cable is OK so if my input jack is connected to ground (and it certainly is) then metal jack which I touch to stop noise is grounded by my cable. So, if this metal banana connector is grounded why I get this noise which stops when I touch metal parts? Huuhhhh...

[deadsnake]

I made a rough schetch of the wiring.

The blue wire connects the shield of your enclosure to the ground trace. This should solve it. But remember to cover the bottom too.

[stand]

To deadsnake:

Thanks for instructions; I am going to find some piece of metal to test it. It could be nice to get rid of ground noise this easy way. If it doesn't help then I'll probably have to find some metal enclosure – I am afraid that I could have problems to ground parts to this thin Al – foil. Anyway, thank you for this picture, pall... Now I cannot make mistake about it.

To Transmogrifox:

Man, thank you for such a detailed answer. I knew that guitar is a perfect antenna but until now it worked just as it should do (no distant radio stations noises until yesterday, ha, ha). It's obvious that I'd have to go for some kind of metal enclosure. Unfortunately here (ex – Yugoslavia) we don't have Radio Shack or Maplin, not to mention Digikey or Mouser...  Our local electronic shop sells metal boxes which are so weak but still expensive... But I think that I could find something appropriate somewhere (you know the problem - when you don't need'em such things are always around your feet but when you really need it – no signs of them...).

I'll try to use this trick with small 47pF on the input jack, I hope it will work. If not, RF - stopper rings probably you mentioned could do the job, but here it is not easy to find some.

I use just 9v battery to avoid problems caused by power supplies.

Your idea to make an atomic shelter to get away from radio noises is great. This way I'd get not just perfect place to play guitar but also life-saving chamber if some lunatic press that red button... (Its bad joke, I know... ;-))

Your advices are so good; I'll see what I can do about this problem.

Btw, can anyone give me any explanation why my pedal gives me much better sound (stable distortion and long sustain) when all parts are in table. As soon as I put it all into (plastic) enclosure distortion becomes unstable and sustain is way shorter... Do you think that I should use 100k resistor instead of gain pot which obviously makes problem when it's close to other 2 pots. I use it on max - position all the time, so...

[Transmogrifox]

“Get hum, unplug guitar.
Still hum, guitar is source.
Cable test, same way”.

I must admit that I cannot understand it (though it’s written in plain English…).
If I have hum with unplugged guitar then how guitar can be source of hum? And, about cable, should it be this way:

Here's what petemore is saying in long form:

When you have your guitar plugged into the pedal through a cable there is noise.  If you unplug your guitar from the cable, and there is no noise, the guitar is the problem.

That part (above) you followed.  The part that threw you is the "Cable, same way" thing.

Now if you had unplugged your guitar from the cable and there is STILL noise, then the problem is not the guitar.  So now you should unplug the cable from the pedal.   If the noise goes away, then it was coming through the cable.  That's the cable test part.

One caveat:  if you have the input jack wired to disconnect power from the pedal when it's unplugged, you'll have to do something to keep it powered when the cable is not plugged into the input jack.

If the noise goes away when you disconnect the guitar or cable, then refer to my post above about filtering the input.  In this case, no amount of shielding or box grounding will help.

If the noise is still there when the pedal is powered, but the input is completely disconnected from the outside world, then the grounded metal enclosure and power supply filtering are your friend.

[stand]

To Transmogrifox:

Yup, it's clear now... This is simple but effective way to see where is source of noise(s). The first thing in the morning I'll check it out so we'll see what's going on... I'd do it right now but at this moment my guitar is not available... Thanks, man!

And also thanks for warning about power breaking when plug is out of jack – my Metal Simplex cannot work without banana plug so some simple unused banana plug will do the job, I think...

I am boring person, I know, but I have to ask again – does anyone know if noise or anything else can diminish sustain and distortion when all parts of pedal are in the box (see above)...

[Transmogrifox]

The noise is very likely causing the diminished sustain.  What has probably happened is that when you box it into the pedal, the longer wires get closer together and closer to components on the board so the RF noise gets injected to a greater degree by the capicitive effect of the close proximity of the wire--may even be some magnetic field stuff happening so it's like an RF transformer.

Whatever the case, the RF signal is banging the rails on your transistors at a very high frequency (turning them on and off real fast), and pretty much just multiplies RF carriers with RF carriers, leaving noise products in the audible spectrum which in turn are multiplied with your guitar when you play and it's all mayhem from there.  Don't worry about the loss of sustain until after you have resolved the noise issue.  If you get rid of the noise issue, and still have the sustain problem when you stick it in the box, then we'll go from there.

If you're into math at all, here's the mathematical explanation for what happens here:

The main assumption I'm making here is that indeed a distortion pedal is a multiplier.  When banged to its extremes, it is a square-law multiplier.  Another way to explain it is in the way of "intermodulation distortion".  I won't go into details about these, but just let the assumption be that indeed the distortion pedal is a multiplier.

cos(A)*cos(B) = (1/2)*cos(A+B) + (1/2)*cos(A-B)

In the case of a time varying signal, then A and B represent something like the following:

A = 2*pi*f₁*t + theta₁
B = 2*pi*f₂*t + theta₂

where f_n is some frequency, and theta_m is some phase angle.

Any signal can be thought to be a sum of cosines of varying phases, frequencies, and angles.  Nothing hard about that, just instead of having the nice

cos(A)*cos(B)

expression, you may have something similar to this:

[k₁cos(A) + k₂cos(2*A) + k₃cos(3*A) +....+k_ncos(m*B) ] * [p₁cos(B) + p₂cos(2*B) + p₃cos(3*B) +....+p_ncos(m*B) ]

Lots of cross products come out of that mess.  An AM radio carrier of perfectly constant amplitude truly is the simple cos(A), but when you have noise and/or radio signal modulated on them and distortion in your system then it's a very messy thing like above.

Here's a simplified example of what may happen in your distortion pedal:

suppose there's a strong AM carrier at around 800 kHz.  Now suppose there's an element of noise at 800,500 Hz.  You multiply these two frequencies together by ramming the rails in your metal pedal, and you have a frequency at 800,500 Hz + 800,000 Hz = 1,600,500Hz (not audible), and one at 800,500 Hz- 800,000 Hz = 500 Hz (very much audible).

There is likely all kinds of noise all over the place, and even many transmitted radio carriers as well + even signal so some of those frequency terms may be components of voice or music, but the deal is that there are a lot of them, and a lot sounds like noise and static...and if one is particularly strong then it sounds like a whine or squeal.

Now take that 500 Hz product from the example above and put some guitar in there.  Now you've multiplied your guitar signal with this and it seriously messes up the sound and potentially the sustain.  When you have a lot of these products at many different frequencies in the audible band, then it really messes things up.

So what you're doing when you add a smallish capacitor shunt to ground on the input is  you bleed all that high frequency garbage off to ground so that it doesn't get into the amplifier where it can be multiplied with itself and your guitar.  At the same time, the capacitor is small enough that it doesn't filter any of the audible frequencies so you don't lose tone by doing it.

[stand]

To prof. Transmogrifox  :

Hmmm, back to school, chalk & blackboard, math...

Yes, I am not bad in math and physics, but I don't have to use cos, sin and tang and everyday so I had to put few drops of oil into my brain cog-wheels to be able to understand what you tried to say about RF, pedal, etc. So here I'll try to recapitulate:

Guitar works like a good antenna so it will pick up all unwanted signals around including RF noise and all other "garbage" on all possible frequencies. When I use it without pedal guitar still does it's "antenna job" but since it is not amplified with anything before it gets to amp signal is more or less "clean" – RF garbage is not audible or is very, very quiet compared to basic signal. When I add pedal into the chain all these unwanted frequencies will appear because those are amplified (or multiplied). All these frequencies make big mess when multiplied so now instead of pure guitar sound signal I've got lots of sounds with different frequencies and amplitudes so it is really sounds chaotic and guitar sound cannot fight against it so it diminishing its relative level (compared to silence when there is no any added noise). The final "nail to the coffin" is a moment when I put everything into one small box – ling wires even makes thing worse by inducing more noise and make even more mess. So, this is why my sustain and good distortion go to hell when I set up everything into the box.

I tried to use the simplest words and I hope that I succeed to understand it well, so let me know about it, please.

So, what I'll try now is – I'll first try to do that simple test to see what brings that noise into the system. I believe that both cable and guitar are here to blame. If it's about guitar or cable I'll first try to ground wires somehow, then I'll see how could I filter it out (I hope that this small cap shunt on input jack can help). If it's about pedal I'll see if I can somehow shield it or I'll try to find some metal enclosure to use it as shield. Idea to use some metal thing to connect it to the ground to see if noise that stops when I touch the strings is diminished is great, I'll try it first. Finally, I have idea to make shorter all wires that don't have to be long (especially from input and output jacks to in and out points on protoboard and also in and out signal ground wires). I'll then try to move them so they stay as far as possible from other wires (which is not easy task in 12 x 7 x 5cm box). I'll try to use shielded wire for at least input and output. But, I understand that all shielding and grounding won't help a lot if RF noise is already picked up by guitar and/or cable, so probably I have to fight against noise on all "fields" (before pedal and inside of it).

I'll let you know what I did about it. So, one "thanks" is such a small award for such a well explanation. I hope that there are lots of pedal DIY-ers who fight their own battle against all kind of noises so I hope that your "in depth" lesion will help them to suppress or maybe even kill that noise-beast. Someone mentioned "Mother Nature" on this forum and said that it's her way to teach us about capacitance, RF noise etc... OK, I agree, but since we learnt it all well she now could be so kind to leave as alone to play without all that hassle, am I right or not?

I am sorry if I was boring with my question but I hope that there are so many good people on this forum who'll find this correspondence interesting and usable. That's probably why are we all coming here, isn't it? 
Thanks again!

Dejan

[Transmogrifox]

It looks like you get the idea. 

To clarify, RF is inaudible no matter which way you look at it.  The human ear cannot hear anything much above 20 kHz.

The reason RF noise causes audible noise is due to the mathematical explanation above:  There is multiplication in a distortion pedal, and some of  the multiplicative cross-terms fall into the audible band.

You were right about the high gain causing the problem.  The high gain amplifies the RF to where the RF signals are clipping, "distorting".  This is what makes the pedal into a multiplier.  If you had an infinite power supply, you would still never hear the RF (but your guitar wouldn't distort either--it would just be really loud). 

Your amp may have some filtering on the input to reject RF noise, so it may be a combination of lower gain, and lower bandwidth that prevent RF signals from multiplying and generating audible noise.

[stand]

Hi!

It will be just quick report...

The most of noise are coming from guitar (say 60%, measured by ear), then from cable (approx 30%) and the rest is coming from pedal (not very much).

I made 3 changes to see what will happen with noise.  I soldered 39pF (I had just this one) ceramic cap on input jack between hot side and ground as proposed. Then I shorted all long wires to reasonable short lenghts and then I conected tone pot to volume pot ditectly to avoid double pot - board -pot connection. This really diminished noise, but I probably need proper guitar grounding to make it all better. I have noticed that sustain is longer when I put gain pot out of the box (when these 2 wires are far from other wires and the board). Since this pot doesn't make much difference (sound is almost the same from max to 10% position and then fades into low distortion which is not very pleasant - sound is diminishing very soon and since it is METAL PEDAL we don't need soft fuzz here) I decided to throw it out and to put 100k resistor instead. Now I have longer sustain and more stable distortion. So, your advices helped much, indeed!

Now I'll have to find some Al-foil or some thin metal plate to use it as shild and to ground everything to it.

I'll let you know how it goes...

Thanks, again! I don't know what I'd do about it without you, guys ...

Dejan

[Transmogrifox]

Speaking of pots...and a nonmetallic enclosure...

You need to solder a wire from ground to the casings of all your pots.  The shaft and metal "can" are probably working like antennas as well.  I'll bet you will be able to put the gain pot back into the circuit if you ground its can.

If they're platic-cased pots there's not much you can do to shield them except to put them into a shielded box--then the foil will help a lot. 

[stand]

All pots on my Simplex are with plastic casings so I have to go for metal housing or some kind of foil-shielding...

[jrc4558]

Can you possibly figure out what's the noise's promary pitch? I mean, just by ear, compared to a tuned guitar, try and find a note (or several notes) that are close in pitch to your noise. That would definitely help to understand where is it really coming from.
Also, check the grounds on your guitar cable and on your guitar itself.

[Sasha Lee]

Hi guys.

I experience exactly the same problem with Metal Simplex and noise/diminished sustain. The difference is that I have 1590a metal box and everything grounded to the box, 2 * 1n4148 diodes and 5089 transistors instead of 3904. I added to the original schematic 1nF cap in parallel with 1M resistor from input to ground to reduce noise and 3.3uF cap from V+ to ground to filter DC. I also changed the input cap from 100nF to 47nF. There is still some radio frequency noise even if nothing pluged to the input and sometimes I get very week signal from my guitar and very loud noise. Here is how my pedal looks like (no volume pot).



I red this topic and some others several times but still can't figure out what could be a problem.
Any suggestions?
Thanks